The spider and the wasp

Tarantulas might look scary, but they pose much less danger than certain smaller species.

By DIANA BARSHAW

September 3, 2009 16:13

spider wasp 88.
(photo credit: )

One evening when Ben was about three years old he came up to me all smiles and excitement. "Look what I have, mommy," he said, with his palm held straight out so I could see. In his hand was a large, dark, hairy spider. It took extreme self-control to stop myself from slapping the creature off his hand. Instead, faking calmness, I gently helped my little son to put the spider down on the floor. I have no memory of what happened next, but most likely my husband and I placed the spider in some container and released it outside. That spider was a tarantula.
Tarantulas are a family of spiders called Theraphosidae, comprising about 900 species, that live around the world in warm climates. They are the largest of all spiders - up to 28 cm. in diameter (the size of a dinner plate). The common name, tarantula, has a strange history. It comes from a port city in the south of Italy, Taranto. However, this area has no Theraphosidae spiders. Instead it was a large unrelated wolf spider (Lycosa tarantula) that was first given the name tarantula.
This wolf spider was thought to cause a malady that could only be cured by dancing wildly, sometimes for days at a time. Actually the wolf spider of Taranto was innocent; its bite hurts for a few minutes, but has no lasting effect. It could be that people blamed this large spider for the bite of the much smaller Mediterranean black widow spider which lives in the area and does have a dangerous bite.
Tarantulas look frightening to humans, who I think are instinctually afraid of all spiders and fear them in proportion to their size. In fact, many smaller spiders - like the black widows and brown recluses - are truly dangerous, while the bite of these huge creatures are not as dangerous or as painful. There are passionate enthusiasts around the world who love tarantulas, have discussion groups about their favorite species and keep them in their homes as exotic pets. Yet there is not a complementary quantity of academic information.
In Israel there are no scientists who have studied the local tarantulas. Perhaps this is because identifying tarantulas to the species level is a specialized and daunting field, and without knowing the species it is hard to conduct an experiment. A taxonomic study published in 2008 by Dr. Jose Guadanucci of the University of SÃ£o Paulo in Brazil and Dr. Richard Gallon from North Wales found that what was once thought to be three species of tarantulas living in Israel are actually all one species. If their analysis is accepted, all the tarantulas here are Chaetopelma olivaceum (parvnit shahor, in Hebrew).
REGARDLESS OF their huge size and fearsome appearance, tarantulas are themselves the prey to a specialized and efficient predator, the spider wasp. Sometimes called tarantula hawks, they are solitary wasps belonging to two genera: Pepsis and Hemipepsis. These insects are large and conspicuous. Most species have bright red, yellow or orange wings with iridescent black or blue bodies. They are impossible to miss.
Several times I watched female Israeli spider wasps of the species Hemipepsis brunnea search for and find a tarantula, sting it with their paralyzing venom and then drag it to their lairs where they deposit an egg onto the still living, but paralyzed spider. The wasp then closes the lair and in some cases camouflages it. The egg develops into a larva that feeds on the living spider. The stuff of horror movies.
In a variation of this story, David Ward and Joh Henschel from the University of British Columbia in Canada studied a different spider wasp (Pseudopompilus humboldti) that lives in the Negev. They found that these wasps placed their paralyzed spider at the entrance of the spider's own nest, exposed to birds and other animals which sometimes ate them. Why would the wasps not do more to protect their developing progeny?
Ward and Henschel hypothesized that temperatures in the Negev were so high that if the wasps didn't place them thus, their larvae would be unable to develop. Sure enough, when the scientists moved the paralyzed spiders to a deeper, more protected area of the nests, the wasp larvae became too hot and died. It was better to risk some predation than the certainty of their larvae dying from excessive heat.
BUT THE adaptations of these wasps are dwarfed by Hymenoepimecis argyraphaga, another solitary wasp studied by Dr. William Eberhard of the Smithsonian Tropical Research Institute in Costa Rica. He found that this wasp actually changes the behavior of the spider for its own benefit. These wasps don't paralyze the spider, instead they stick their egg on an active spider and the wasp larva feeds on the spider's juices, much like a tick sucks blood. However, right before the larva is about to build a cocoon so that it can metamorphose into an adult wasp, it injects the spider with a drug. Suddenly instead of building a typical web, the spider builds a tangled structure that is devoid of the sticky threads normally used to catch insects, and is instead perfect to carry the wasp's cocoon. After doing the wasp's bidding the spider dies.
So the wasps prey on the spiders, sometimes with extraordinary powers, but what preys on the wasps? It turns out nothing preys on these creatures; they live la dolce vita at the very pinnacle of the food chain.
Dr. Justin Schmidt of the Southwestern Biological Institute in Arizona showed why. He collected large numbers of wasps and found that they have huge quantities of venom with a large, curved, sharp stinger surrounded by strong muscles. Schmidt stated several times that no sane scientist would willingly get stung just to make an assessment of the sting, but he was inadvertently stung several times while collecting. Here is his description of how it feels: "The pain was instantaneous, electrifying, excruciating and totally debilitating."
The good news is that the wasps only sting to subdue their prey or to protect themselves; they are not aggressive. Also good news for us vertebrates is that while the venom causes extreme short-term pain, it has no long-term side effects. It is clear why the wasps advertise themselves with their bright and beautiful coloration and why all potential predators recognize them and steer clear.
Next time you see a beautiful red-winged wasp and a huge ugly tarantula, remember appearances can be deceptive. The sting of the wasp might be worse than the bite of the spider!
The writer has a PhD in animal behavior and ecology. www.Dianabarshaw.com

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